Abstract
We photoexcite SrTiO3 and EuTiO3 in their purely soft-mode-driven structurally distorted phase and trace the structural order parameter via ultra-short x-rays. We observe a rapid decay for SrTiO3 and an intriguing transient enhancement for EuTiO3.
Highlights
We study the ultrafast photoinduced dynamics of the structural order parameter in a class of perovskites where phonon-phonon interactions are believed to be the primary mechanism of the thermodynamic transition
EuTiO3 (ETO) and SrTiO3 (STO) undergo a soft-mode-driven [1,2] structural phase transition from cubic to tetragonal symmetry given by an antiferrodistortive (AFD) rotation of the oxygen octahedra around the Ti ions (Fig. 1a)
Our results indicate that in systems with phonon-mediated equilibrium phase transitions electronic interactions with the soft mode play an important role in the nonequilibrium case
Summary
We study the ultrafast photoinduced dynamics of the structural order parameter in a class of perovskites where phonon-phonon interactions are believed to be the primary mechanism of the thermodynamic transition. EuTiO3 (ETO) and SrTiO3 (STO) undergo a soft-mode-driven [1,2] structural phase transition from cubic to tetragonal symmetry given by an antiferrodistortive (AFD) rotation of the oxygen octahedra around the Ti ions (Fig. 1a). This structural transition does not involve electronic ordering (i.e. no charge/orbital order, superconductivity) and the soft-mode double-well potential is purely given by phonon occupations [3]. We employ above-bandgap femtosecond pulses to excite two perovskites with similar structural distortion out of the low-temperature equilibrium phase and monitor the subsequent dynamics of the order parameter via the intensity of distortioninduced superlattice (SL) reflections using ultrashort hard x-ray pulses (Fig 1b). The study on ETO was conducted on a PLD grown 40 nm ETO film on STO (100) substrate at LCLS/SLAC
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